OSI LAYERS ccna OSI Model OSI means Open

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OSI LAYERS ccna

OSI LAYERS ccna

OSI Model � OSI means Open System Interconnect model. � Developed by the International

OSI Model � OSI means Open System Interconnect model. � Developed by the International Organization for Standardization in 1974. � It consists of seven layers. � Each layer has a different but specific processing function. 2

OSI Model Layers Layer - 7 Application Layer - 6 Presentation Layer - 5

OSI Model Layers Layer - 7 Application Layer - 6 Presentation Layer - 5 Session Layer - 4 Transport Layer - 3 Network Layer - 2 Data Link Layer - 1 Physical Upper Layer or Software Layer Heart of OSI Lower Layer or Hardware Layer 3

Application Layer Presentation Application Layer is responsible for providing Networking Services to the user.

Application Layer Presentation Application Layer is responsible for providing Networking Services to the user. It is also known as Desktop Layer. Identification of Services is done using Port Numbers. Session Ports are Entry and Exit Points to the Layer Application Transport Network Total No. Ports 0 – 65535 Reserved Ports 0 – 1023 Open Client Ports 1024 – 65535 Data Link Physical 4

Example of HTTP request http: //www. zoomgroup. com Client Web Server 5

Example of HTTP request http: //www. zoomgroup. com Client Web Server 5

Example of HTTP request HTTP Request Received HTTP Reply http: // www. zoomgroup. com

Example of HTTP request HTTP Request Received HTTP Reply http: // www. zoomgroup. com http: //www. zoomgroup. com Webpage Client HTTP Request Listen on Port 80 Sending HTTP Reply Webpage Web Server 6

Example of FTP request ftp: //ftp. microsoft. com Client FTP Server 7

Example of FTP request ftp: //ftp. microsoft. com Client FTP Server 7

Example of FTP request FTP Request Received FTP Reply ftp: //ftp. microsoft. com Client

Example of FTP request FTP Request Received FTP Reply ftp: //ftp. microsoft. com Client FTP Request Listen on Port 21 Sending FTP Reply FTP Server 8

Examples of Networking Services Service Port No. HTTP 80 FTP 21 SMTP 25 TELNET

Examples of Networking Services Service Port No. HTTP 80 FTP 21 SMTP 25 TELNET TFTP 23 69 9

Data flow from Application Layer Data Application 80 21 25 53 67 69 Presentation

Data flow from Application Layer Data Application 80 21 25 53 67 69 Presentation Session Transport Network Data Link Physical 10

Presentation Layer Application Presentation Layer is responsible for converting data into standard format. Examples

Presentation Layer Application Presentation Layer is responsible for converting data into standard format. Examples : ASCII, EBCDIC, JPEG, MPEG, BMP, MIDI, WAV, MP 3 Session Transport Network Data Link Following tasks are perform at Presentation layer : Encoding – Decoding Encryption – Decryption Compression – Decompression Physical 11

Data flow from Presentation Layer Application Data Presentation Data Session Transport Network Data Link

Data flow from Presentation Layer Application Data Presentation Data Session Transport Network Data Link Physical 12

Session Layer Application Presentation Session Layer is responsible for establishing, maintaining and terminating session.

Session Layer Application Presentation Session Layer is responsible for establishing, maintaining and terminating session. Session ID works at Session Layer. Session Examples : Transport RPC Remote Procedure Call SQL Structured Query Language NFS Network File System Network Data Link Physical 13

Data flow from Session Layer Application Data Presentation Data Session Data Transport Network Data

Data flow from Session Layer Application Data Presentation Data Session Data Transport Network Data Link Physical 14

Transport Layer Application Presentation Session Transport Network Transport Layer is responsible for end-toend connectivity.

Transport Layer Application Presentation Session Transport Network Transport Layer is responsible for end-toend connectivity. It is also known as the heart of OSI Layers. Following tasks are performed at the Transport Layer : - • Identifying Service • Multiplexing & De-multiplexing • Segmentation • Sequencing & Reassembling • Error Correction Data Link • Flow Control Physical 15

Identifying Service TCP UDP • Transmission Control Protocol • User Datagram Protocol • Connection

Identifying Service TCP UDP • Transmission Control Protocol • User Datagram Protocol • Connection Oriented • Connection Less • Acknowledgement • No Acknowledgement • Reliable • Unreliable • Slower • Faster • Port No. 6 • Port No. 17 • e. g. HTTP, FTP, SMTP • e. g. DNS, DHCP, TFTP 16

Multiplexing & De-multiplexing Application Presentation Session 80 21 25 53 67 69 Transport TCP

Multiplexing & De-multiplexing Application Presentation Session 80 21 25 53 67 69 Transport TCP - 6 UDP - 17 Network Data Link Physical 17

Segmentation Hello! How are you ? Hello! How Are A You ? B 18

Segmentation Hello! How are you ? Hello! How Are A You ? B 18

Sequencing & Reassembling Hello! How are you ? Hello! How are ? you You

Sequencing & Reassembling Hello! How are you ? Hello! How are ? you You Hello! Are? You Hello! A Hello! How Are ? You you Hello! How ? are Are ? B 19

Sequencing & Reassembling Hello! How are you ? A Hello! How are you ?

Sequencing & Reassembling Hello! How are you ? A Hello! How are you ? Hello! How Are You Hello! How are you ? ? 1/5 2/5 3/5 4/5 5/5 You Hello! How ? Are 4/5 1/5 2/5 5/5 3/5 B 20

Error Correction Segment Missing Hello! How are you ? Hello! 1/5 A How 2/5

Error Correction Segment Missing Hello! How are you ? Hello! 1/5 A How 2/5 Are You Hello! How are you ? ? 3/5 4/5 5/5 You Hello! How ? Are 4/5 1/5 2/5 5/5 3/5 B 21

Flow Control - Windowing Ack-Rec-3 Sending 3 Ack. Sending window Received-4 5 -window A

Flow Control - Windowing Ack-Rec-3 Sending 3 Ack. Sending window Received-4 5 -window A PC-A Received 43 can send 4 Segment at awindow time to PC-B B 22

Data floaw from Transport Layer Application Data Presentation Data Session Data Transport TH Data

Data floaw from Transport Layer Application Data Presentation Data Session Data Transport TH Data Segment Network Data Link Physical 23

Network Layer Presentation Network Layer is responsible for providing best path for data to

Network Layer Presentation Network Layer is responsible for providing best path for data to reach the destination. Logical Addressing works on this layer. Router is a Network Layer device. Session It is divided into two parts Application • Routed Protocols Transport Network e. g. IP, IPX, Apple Talk. • Routing Protocols e. g. RIP, IGRP, OSPF, EIGRP Data Link Physical 24

Routed Protocols Segment Hello! How are you ? Source IP 192. 168. 1. 1

Routed Protocols Segment Hello! How are you ? Source IP 192. 168. 1. 1 Hello! How are you ? Destination Segment IP 192. 168. 1. 2 A 192. 168. 1. 1 B 192. 168. 1. 2 25

Routing Protocols www. zoomgroup. com A 26

Routing Protocols www. zoomgroup. com A 26

Data flow from Network Layer e. g. Router Application Data Presentation Data Session Data

Data flow from Network Layer e. g. Router Application Data Presentation Data Session Data Transport Segment Network Packet NH Segment Data Link Physical 27

Datalink Layer Application Presentation Session Transport Network Data Link Datalink Layer is Layers :

Datalink Layer Application Presentation Session Transport Network Data Link Datalink Layer is Layers : divided into two Sub • LLC – Logical Link Control It talks about Wan protocols e. g. PPP, HDLC, Frame-relay • MAC – Media Access Control It talks about Physical Address. It is a 48 bit address i. e. 12 digit Hexadecimal Number. It is also responsible for Error Detection Devices working on Data Link Layer are Switch, Bridge, NIC. Physical 28

Error Detection – CRC Check Packet PC-A CRC No. 33333 Hello! How PC-B are

Error Detection – CRC Check Packet PC-A CRC No. 33333 Hello! How PC-B are you ? Source MAC 00 -20 -18 -C 0 -07 -71 CRC No. 11114 Error 00000 33333 11114 46323 99434 43434 99323 55434 89696 22222 32434 Detected Destination Packet MAC Error Detected 00 -20 -18 -C 0 -07 -72 A For Error Correction Contact Source Transport layer 192. 168. 1. 1 00 -20 -18 -C 0 -07 -71 B 192. 168. 1. 2 00 -20 -18 -C 0 -07 -72 29

Error Detection – CRC Check Packet Source MAC 00 -20 -18 -C 0 -07

Error Detection – CRC Check Packet Source MAC 00 -20 -18 -C 0 -07 -71 Hello! How are you ? 20202 11114 46323 99434 43434 99323 55434 89696 22222 32434 00000 Destination Packet MAC 00 -20 -18 -C 0 -07 -72 A 192. 168. 1. 1 00 -20 -18 -C 0 -07 -71 B 192. 168. 1. 2 00 -20 -18 -C 0 -07 -72 30

Data flow from Data Link Layer e. g. Switch Application Data Presentation Data Session

Data flow from Data Link Layer e. g. Switch Application Data Presentation Data Session Data Transport Segment Network Packet Data Link Packet DT DH Frame Physical 31

Physical Layer Application Presentation Session Transport Physical Layer is responsible for electrical, mechanical and

Physical Layer Application Presentation Session Transport Physical Layer is responsible for electrical, mechanical and procedural checks. Data will be converted into Binary (i. e) 0’s & 1’s. Data will be in the form of electrical pulses if it is Coaxial or Twisted Pair cable and in the form of Light if it is Fiber Optic Cable. Devices working at Physical Layer are Hubs, Repeaters, Cables, Modems etc. Network Data Link Physical 32

Physical Layer Example Frame Hello! How are you ? 10101010 Frame A 010101010101010 01010101010101

Physical Layer Example Frame Hello! How are you ? 10101010 Frame A 010101010101010 01010101010101 B 33

Data flow from Physical Layer e. g. Hub Application Data Presentation Data Session Data

Data flow from Physical Layer e. g. Hub Application Data Presentation Data Session Data Transport Segment Network Packet Data Link Frame Physical Bits 34

Data Encapsulation & De-capsulation A B Application Data Application Presentation Data Presentation Session Data

Data Encapsulation & De-capsulation A B Application Data Application Presentation Data Presentation Session Data Session Transport TH Data Segment TH Data Transport TH Network Packet NH Segment Packet. Segment NH Network NH Data Link Frame DH Packet DT Packet Data Link DH DT Physical Bits Physical 35

Comparing OSI with TCP/IP Layers OSI Layers TCP/IP Layers Application Presentation Application Session Transport

Comparing OSI with TCP/IP Layers OSI Layers TCP/IP Layers Application Presentation Application Session Transport Network Internet Data Link Physical Network Access 36

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